Are 3d assets purchased from assets website, say turbosquid editable?
Yes they are, 

Re TURBOSQUID


  Do I have the right to modify Stock Media Products?
  
  Yes. You may modify them to make your Creations. Please keep in mind
  that no matter how much you modify a Stock Media Product, it still may
  only be distributed as a Creation and is subject to the rules of the
  Royalty Free License.


please read the TURBO SQUID licensing terms to be sure you can use them for your intended purpose.